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1.
This work reports the principle, advantage, and limitations of analytical photoion spectroscopy which has been applied to dissociative photoionization processes for diatomic molecules such as H2, N2, CO, and NO. Characteristic features observed in the differential photoion spectra are summarized with a focus on (pre)dissociation of(i) multielectron excitation states commonly observed in the inner valence regions,(ii) shape resonances, and(iii) doubly charged parent ions. Possible origins for negative peaks in the differential spectra are discussed. This spectroscopy is applied to the reported photoion branching ratios for D2 (and H2 at high energies). The main findings are as follows: (1) The direct dissociation of theX 2Σ g + (1sσ g ) state of D 2 + , the two-electron excited state1Σ u + (2pσ u 2sσ g ) of D2, and the2Σ u + (2pσ u ) state of D 2 + appear clearly in the differential spectrum, as previously observed for H2. (2) Decay of H 2 + (D 2 + ) to H+ (D+) above 38 eV is due to the direct dissociation of highly excited states of H 2 + (D 2 + ) such as the2Σ g + (2sσ g ) and high-lying Rydberg states converging on H 2 2+ (D 2 2+ ). (3) In the ionization continuum of H 2 2+ (D 2 2+ ) peculiar dissociation pathways are observed. The differential photoion spectra for O2 derived from the reported photoion branching ratios are also presented. The (pre)dissociation of theb 4Σ g ? ,B 2Σ g ? , III2Π u ,2Σ u ? , and2,4Σ g ? states of O 2 + appears as the corresponding positive values in the spectra in accord with previous observations. Some other dissociation pathways possibly contributing to the spectra are discussed including dissociative double ionization.  相似文献   

2.
We discuss the stability of doubly charged Auclusters. From a calculation using semi-empirical linear combination of atomic-orbitals (LCAO) method, we conclude that Au 2 2+ in an excited state (3Σ u + or1Σ u + ) is metastable with an energy barrier of about 0.3 eV. In the ground state (1Σ g + ) Au 2 2+ is unstable, except for small values of Δ(=ε s d ) (difference between thes andd atomic energy levels of Au), when a very shallow minimum appears in the binding energy curve. These results are critically discussed and compared with those obtained by different calculations.  相似文献   

3.
As a first attempt to study the stability of the H*4 (C3v ) cluster we have used the MRD-CI method and a medium size basis set to calculate various sections of the potential energy surfaces of its ground and first excited states. We show that these correlate to the (X 1Σ g 1 X 1Σ g + ) and (X 1Σ g + B 1Σ u + ) states of the two H2 constituents respectively. Finally, we report on the calculation of the diabatic matrix elements of the vibronic interaction in the region of the avoided crossing which is crucial to the stability of H 4 + .  相似文献   

4.
5.
Potential curves for the ground (2Σ u + ) and the three lowest excited states of the Xe 2 + dimer ion (2Π g ,2Π u ,2Σ g + ) have been calculated using pseudopotentials in MRD-CI (multi-reference single anddouble excitationconfigurationinteraction) calculations. Spin-orbit interaction — leading to the six states 1.(1/2) u , 1.(3/2) g , 1.(3/2) u , 1.(1/2) g , 2.(1/2) u , 2.(1/2) g — has been taken into account using a semiempirical technique [1]. Subsequently, starting with a relaxed Xe 2 + ion in its ground state, the potential energy surface for the system Xe-Xe 2 + was studied. We found that the collinear approach of the Xe atom leads to the most stable geometry. This is a linear symmetric molecule with bond lengths of 6.38 bohr. In the bestT-shaped structure, the Xe atom is 7.83 bohr away from the midpoint of the Xe 2 + (r=6.1 bohr) dimer. The calculated binding energy of 0.25 eV for the equilibrium structure of the Xe 3 + molecule (i.e. the linear symmetric geometry), is in very good agreement with experimental results of 0.27 ± 0.02 eV [2].  相似文献   

6.
Synchrotron radiation is used to selectively excite the chlorine molecule in the VUV spectral range. Stationary fluorescence spectra of the 11Σ u + state are observed following primary excitation of 11Σ u + and 21Σ u + . The bound-free part of the spectra is analysed with the aid of quantum mechanical computer simulations. A potential energy curve is constructed which is an approximation of the adiabatic double well potential energy curve of the 11Σ u + state. The inner well is characterized byT e =(73428±50) cm?1,r e =(1.85 ± 0.05) Å; for the outer well holdT e =(64631±50) cm?1,r e =(2.57±0.05) Å, ω e =(261±5) cm?1, ω e x e =(0.668±0.01) cm?1 (35Cl2;v′<30). The potential energy curve is successfully checked with fluorescence excitation spectra. Within the error limits, the results of a former synchrotron radiation study are verified. It is ruled out, that the Cl2 “γ-state” recently observed with laser spectroscopic methods, can be attributed to the outer well of 11Σ u + .  相似文献   

7.
Photofragment spectroscopy of N 2 + has been studied in the wavelength range 343–404 nm using an excimer-pumped dye laser with a spectral resolution of 0.2 cm?1. The observed bands are assigned to transitions from thev″=23?26 levels of theX 2Σ g + state to highlying rovibrational levels (v′≈46–48) of theB 2Σ u + state, forming quasibound (predissociating) states above the dissociation limit N+(3 P)+N(4 S 0). Measurement of the photofragment kinetic energies allows to establish an absolute energy scale for the transitions with respect to the dissociation limit. Molecular constants for the lower and upper states of the observed transitions are determined. The measurements allow the first direct determination of the N 2 + dissociation energyD 0 0 (N 2 + ). Some high-resolution (0.04 cm?1) measurements show the fine-structure splitting and lifetime broadening of the excitation lines.  相似文献   

8.
The transitions between Ar 2 * (5p) and Ar 2 * (4sΣ u) have been investigated by absorption spectrometry. The fine structure of the Ar 2 * (5p 3 Π g) was attributed to a predominantly Hund’s case a coupling. A spin orbit coupling constant of A = (9.8±0.3) cm-1 results. Absorption by the singlet system allows one to determine the triplet/singlet splitting between the Ar 2 * (4s Σ u) states to be (540 ± 100) cm-1. The transition probabilities of the Ar 2 * (5p) and Ar 2 * (6p) levels were determined by saturation spectrometry yielding values between (0.2–2.5) · 106 s-1.  相似文献   

9.
Rotational-vibrational transitions of the triplet system 13Σ g + ← 13Σ u + of the Na2 molecule have been investigated around $\bar v = 13970 cm^{ - 1} $ by Doppler-free polarization spectroscopy in a heat pipe and by resonant two-step photoionization in a collimated cold argon beam, seeded with sodium vapor. The fine- and hyperfine structure of the transitions is partly resolved. The analysis of the measured spectra and a theoretical discussion of the expected multiplet structure yields the rotational constantsB v (v′=17)=0.0866(4) cm?1 for the upper andB v (v″=0)=0.0533(4) cm?1 for the lower state. The difference Δb=b(3Σ u )?b(3Σ g ) of the hyperfine coupling constantsb turns out to be Δb=80 MHz.  相似文献   

10.
The7Li2 21 Σ u + X 1 Σ g + electronic transition has a bound-bound and a bound-free part due to the double minimum nature of the upper 21 Σ u + state. We have studied this transition both experimentally and by performing spectral simulations. When inner well was excited the bound-free part at 4525 Å was observed due to the collisions between Li 2 * and argon. We found that when levels above the barrier are excited the bound-free emission is strongly affected by collisional relaxation of Li 2 * by Li atoms. Conditions for the observation of the bound-free part are discussed.  相似文献   

11.
The accuracy for the direct measurement of the dissociation energy of the N 2 + B2Σ u +-state was significantly improved by using frequency doubled laser light, which enables the authors to excite from lowerv″-levels and additionally to calibrate the fundamental laser wavelength with an iodine cell. The obtained value is:D 8(N 2 + )=70248±6 cm?1.  相似文献   

12.
Guided ion beam mass spectrometry is used to measure the cross sections as a function of kinetic energy for reaction of SiH4 with O+(4S), O 2 + (2Πg,v=0), N+(3P), and N 2 + (2Σ g + ,v=0). All four ions react with silane by dissociative charge-transfer to form SiH m + (m=0?3), and all but N 2 + also form SiXH m + products where (m=0?3) andX=O, O2 or N. The overall reactivity of the O+, O 2 + , and N+ systems show little dependence on kinetic energy, but for the case of N 2 + , the reaction probability and product distribution relies heavily on the kinetic energy of the system. The present results are compared with those previously reported for reactions of the rare gas ions with silane [13] and are discussed in terms of vertical ionization from the 1t 2 and 3a 1 bands of SiH4. Thermal reaction rates are also provided and dicussed.  相似文献   

13.
Femtosecond time resolved pump-probe experiments studying wave packet dynamics in the (2)1Σ u + double minimum state of Na2 are reported. The experiments were performed in a molecular beam with ion Time of Flight (TOF) detection. By Fast Fourier Transformation (FFT) of the observed time domain data the energy spacings of the coherently coupled vibrational levels in the (2)1Σ u + potential are obtained with an accuracy of 0.02 cm?1, although an ultrafast laser source with its inherent spectral width was used in the experiment. The wavelengths of the pump and probe laser pulses are chosen such that in this two color experiment we can control ionisation versus ionisation induced fragmentation. In order to study the influence of the potential barrier on a vibrational wave packet motion we performed simulations based on time dependent quantum calculations.  相似文献   

14.
Non-empirical calculations of CASSCF energies, electric dipole moments, Einstein coefficients, matrix elements of the operator of spin-orbital interaction between states of different multiplicity in a model complex 6,8[Mn-O2] of C 2v symmetry have been made in 3-21G, 6-31G, 6-31G** basis sets. The crosssections of the potential energy surface (PES) of the ground and excited states were built. It is found that oxygen bonding to manganese is possible when excited atoms of manganese collide with molecular oxygen, singlet oxygen with Mn[6 S 5/2] atoms, or in a close contact O2[X3Σ g ? ] + Mn[6 S 5/2] and is determined by charge transfer states 6,8CTS(Mn+O 2 ? ). Mechanisms of singlet oxygen activation/deactivation are determined by a considerably increased probability of electric dipole transitions b 1Σ g + ?a 1Δg, a 1Δg?X3Σ g ? , b 1Σ g + ?X3Σ g ? induced in oxygen in the collision process.  相似文献   

15.
New data on enthalpy and entropy contributions to the energy barrier of β-pinene thermal isomerization were obtained. The rate of β-pinene conversion is higher in supercritical EtOH (P = 120 atm) than in the gas phase (P ≤ 1 atm, without solvent, or for inert carrier gas N2) at equal temperatures. The highest activation energy E Σ of total β-pinene conversion is also observed in reactions in the supercritical (sc) condition. Activation parameters ΔH Σ # , ΔS Σ # , and ΔG Σ # depend strongly on the reaction pressure. Thus, at P ≤ 1 atm (gas-phase reaction) the values of ΔS Σ # are negative, while at sc conditions at P = 120 atm is positive. The linear dependences lnk Σ0 ? E Σ and ΔS Σ # ? ΔS Σ # indicate an isokinetic relation (IKR) and enthalpy-entropy compensation effect (EEC). The isokinetic temperature was calculated (T iso = 605.5 ± 22.7 K). It was shown that elevation of temperature reduces the value of ΔG Σ # (T) upon sc thermolysis only, whereas in all gas-phase reactions ΔG Σ # (T) increases. At equal reaction temperatures, the greatest values of K eq # (T) proved to be typical for thermolysis in sc-EtOH. We hypothesize that the rate of total β-pinene conversion increases dramatically due to a considerable shift in equilibrium toward higher concentrations of activated complex y TS # . A detailed analysis of activation parameters shows that the IKR and EEC coincide, evidence of a common mechanism of β-pinene conversion observed under different reaction conditions, including thermolysis in sc-EtOH.  相似文献   

16.
Quantum chemical ab initio calculations have been performed for the vertical excitation energies and oscillator strengths of all low-lying electronically excited states of small helium cluster ions, He n + ,n=2, ..., 7. The geometrical structures of the ions were fixed at the equilibrium geometries of the respective ground states, for He 4 + and He 5 + also one alternative structure was considered. The low-lying excited states can be classified into two categories: the electronic transition can occur either within the central He 2 + or He 3 + unit or from the peripheral weakly bound He atoms to this unit. The latter transitions are very weak (f≈0.001), closely spaced, with vertical excitation energies of about 5.7 eV. The He 2 + and He 3 + units have strong transitions at 9.93 and 5.55 eV, respectively; these transitions are only slightly blue-shifted if He 2 + or He 3 + are placed as “chromophores” into the centre of a larger He n + cluster. The large difference in the vertical excitation energy of the strong transition should enable an experimental decision of the question whether the cluster ions have He 2 + or He 3 + cores.  相似文献   

17.
Within the adiabatic channel treatment of ionmolecule capture we have calculated the low temperature capture rate constants of N2(1Σ g + ) and O2(3Σ g ? )in collisions with positive and negative ions. In both cases, the charge-quadrupole and the anisotropic charge-induced dipole interactions produce noticeable deviations from the Langevin rate constant. The rate constants calculated with account for the anisotropic interaction, in addition, are substantially affected by nuclear symmetry; in the case of O2(3Σ g ? ), the fine-structure spin-spin interaction strongly manifests itself in the rate constants.  相似文献   

18.
LCGTO-MP-LSD calculation was performed for the ground and several low-lying excited states of homo- (N2, P2, As2, and Sb2) and hetero-nuclear (PN, AsN, AsP, AsSb, SbN, and SbP) groupVA diatomics. For all the systems the ground state is found to be1Σ+. For N2 and P2, the1Σ g + ground state is followed by the3Σ u + ,3Π g ,3Δ u ,1Π g , and1Δ u low-lying exited states while for As2 the order is found to be3Σ u + ,3Δ u ,3Π g ,1Δ u ,1Π g . Finally for Sb2 the relative stability of excited states is3Σ u + ,3Δ u ,1Δ u ,3Π g ,1Π g . For the hetero-nuclear diatomics the1Σ+ ground state is, in the case of PN, AsN, AsP, SbN, and SbP, followed by the3Σ+,3Δ,3Π,1Π and1Δ low-lying excited states while for the AsSb diatomic an inversion of stability of the two last singlets occurs. The calculated spectroscopic parameters (Re, ωe, andDe) are in good agreement with all the available experimental results while, theTe values are overestimated by about 0.5 eV. Mulliken population analysis shows that both homo- and hetero-nuclear groupVA diatomics are essentially triple bonded systems.  相似文献   

19.
Laser excitation spectroscopy is performed on K2 molecules produced in a supersonic molecular beam. 83 vibrational levels of the 21 Σ u + state are observed under conditions permitting rotational resolution. The 21 Σ u + state is partially analysed and its preliminary potential curve is compared with theoretical calculations.  相似文献   

20.
Rydberg states of potassium dimer have been studied in a crossed laser-molecular beam experiment. The K2 molecules were formed in a supersonic expansion and excited by low-power cw dye laser. Two different excitation schemes have been used: The first scheme uses a single mode ring dye laser to induce near resonant two-photon transitions while in the second scheme stepwise excitation with two dye lasers is used. In each case excitation of Rydberg levels was detected by monitoring the ionization signal resulting from three-photon absorption. We report a detailed study of 700 two-photon resonances between 625 nm and 650 nm. Most of these signals can be assigned to transitions from the X1σ g + to1σ g + ,1Π g , and g states, which are all enhanced by the B1Π u intermediate state. Accurate rotational constants are given for the populated vibrational levels of these states. By stepwise excitation of Rydberg levels via theB 1Π u state we identify 3 series of Rydberg states as1Δ g (4S+nD),1Σ g + (4S+nD), and1Σ g + (4S+nS) with principal quantum numbers 7≦n≦20. Molecular constants of these and other observed but as yet unidentified states are given; quantum defects and dissociation energies are discussed.  相似文献   

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